The invention relates to a method for operating a hybrid vehicle comprising an internal combustion engine and an electrical machine for driving the vehicle, and also to a control device, which corresponds to the method, for controlling the operation of a hybrid vehicle.
In a hybrid vehicle of this kind, the internal combustion engine is supplied with fuel (for example gasoline or diesel) from a fuel tank, wherein the fuel filling level of the fuel tank is determined using a fuel filling level sensor. The electrical machine is supplied with electrical energy from an energy store (for example a battery or a capacitor).
The vehicle can be driven in the purely electric mode, with the internal combustion engine switched off, by means of the electrical machine.
Document DE 10 2012 108 485 A1 discloses a method for operating a hybrid vehicle comprising an internal combustion engine and an electrical machine, wherein the hybrid vehicle can be driven in a purely electric manner by means of the electrical machine when the fuel tank for supplying fuel to the internal combustion engine is empty. When the internal combustion engine fails when the fuel tank is empty, continued driving of the hybrid vehicle in a purely electric manner is possible only under the condition that restarting of the hybrid vehicle is initiated by the driver. To this end, the ignition of the internal combustion engine is preferably first switched off and then switched on again.
In the case of a hybrid vehicle of this kind, depending on the design of the fuel filling level sensor, the sensor cannot detect a certain residual quantity of fuel in the tank and it is indicated to the drive control system that the fuel tank is already empty even though a certain quantity of fuel is still present. When the sensor signals an empty tank, the internal combustion engine is shut off and the vehicle is only driven in the purely electric mode using the electric motor until the state of charge (SOC) of the energy store of the electric drive has fallen to such an extent that the vehicle can no longer be driven in the purely electric mode either. For as long as the vehicle is not refueled with a certain minimum quantity of fuel and the filling level does not reach a specific minimum level again (for example at least 5 l of fuel), the drive control system prevents restarting of the internal combustion engine, while the vehicle cannot be driven by means of the electrical machine for as long as the state of charge of the energy store is too low.
A manner of operation of this kind has the disadvantage that the vehicle can no longer move when it is indicated that the fuel tank is empty and when the state of charge of the electrical energy store is too low, even though there is still a sufficient residual fuel in the tank to move a certain distance, for example in order to reach a gas station or an electrical charging station. In the event of an emergency situation or a hazardous situation, it could be of great importance to still use this residual quantity of fuel in the tank and to still operate the vehicle by means of the internal combustion engine for a certain residual running distance.
Furthermore, it is disadvantageous that, in the event of a fuel tank that has run to empty, the driver, when refueling, can fill considerably less fuel into the tank than expected, for example only 42 liters instead of a specified tank volume of 45 liters. This may lead to the driver becoming irritated since the driver expects to be able to run the tank to completely empty.
An object of the invention is to specify an operating method, which is improved in relation to the above, for operating a hybrid vehicle and a correspondingly improved control device for controlling the operation of a hybrid vehicle in which residual fuel in the tank can still be used.
This object may be achieved by the features of the independent patent claims. Advantageous embodiments are described in the dependent claims. It should be noted that additional features of a patent claim which is dependent on an independent patent claim can form an invention on its own and independently of the combination of all of the features of the independent patent claim without the features of the independent patent claim or only in combination with some of the features of the independent patent claim, which invention can be made part of the subject matter of an independent claim, a divisional application or subsequent application. This applies in the same way to technical teachings which are described in the description and can form an invention which is independent of the features of the independent patent claims.
A first aspect of the invention relates to a method for operating a hybrid vehicle comprising an internal combustion engine and an electrical machine for driving the hybrid vehicle. The hybrid vehicle is typically a so-called parallel hybrid in which both the electrical machine and the internal combustion engine act on the drive train; in this case, it can also be provided, for example, that the internal combustion engine and the electrical machine act on different vehicle axles (this is also called an axle hybrid). The hybrid vehicle is preferably a plug-in hybrid vehicle, wherein the energy store of the electric drive can be charged externally by means of a power supply system.
The internal combustion engine is supplied with fuel (for example gasoline or diesel) from a fuel tank, wherein the fuel filling level of the fuel tank is determined using a fuel filling level sensor. The fuel filling level sensor may be, for example, a sensor which measures the filling level directly, for example a fuel filling level sensor with a float of which the vertical height can be measured (for example in the form of an electrical resistor which is related to the vertical height). As an alternative, a fuel filling level sensor which operates by means of throughflow sensors would also be conceivable: in this case, the drawn and added quantity of fuel is measured and the filling level is calculated from this.
The electrical machine is supplied with electrical energy from an energy store (for example from a battery or a capacitor). The vehicle supports a purely electric mode, in which the vehicle is driven by means of the electrical machine with the internal combustion engine switched off.
According to the method, it is first established that the fuel filling level sensor indicates that a lower filling level has been reached or undershot. The lower filling level preferably corresponds to an empty fuel tank, wherein, in this case, it is established that fuel filling level sensor indicates an empty fuel tank. As already stated at the outset, in spite of a fuel tank being indicated as empty, there is however typically still a certain quantity of fuel in the tank. However, the method according to the invention is not restricted to the case of a fuel tank which has been identified as empty by the fuel sensor.
In response to this, the internal combustion engine is switched off and the vehicle is driven in the purely electric mode, with the internal combustion engine switched off, by means of the electrical machine. When the internal combustion engine is switched off, the driver is preferably provided with an, in particular optical, warning message, for example that an internal combustion engine-operated range is no longer available.
The method according to the invention is characterized in that, after a purely electric mode of the vehicle (for example until the driver stops the vehicle on account of a lack of electrical operating capability or the vehicle breaks down), the internal combustion engine is switched on again and the vehicle is driven by means of the internal combustion engine in the special mode with the internal combustion engine switched on, provided that one condition for the special mode are satisfied. There may also be a plurality of conditions which all have to be satisfied so that the internal combustion engine can be switched on and the vehicle can be driven in the special mode by means of the internal combustion engine.
When the one or the several conditions for the special mode are present, the method according to the invention therefore allows the internal combustion engine to be restarted and the remaining residual fuel to be used in the special mode, for example in order to reach a gas station.
Since the residual fuel can be at least partially, preferably completely used, irritation of the driver when refueling is avoided since, when refueling, the driver is aware of the residual quantity of force still located in the tank (this can be approximately zero under certain circumstances during refueling) which corresponds, together with the quantity of fuel with which the tank is filled, to the specified tank volume of the vehicle.
The method according to the invention is not restricted to the case of a fuel tank which has been identified as empty by the fuel sensor, but rather could also be used when the internal combustion engine is switched off, for example when a lower filling level of 1 liter of fuel which is detected by the sensor is undershot, so that the vehicle is driven in the purely electric mode. According to the invention, the remaining residual fuel (for example 1 liter) can be at least partially used later when the internal combustion engine is switched off if the one or more conditions for the special mode are satisfied. The lower filling level preferably corresponds to a value of 0 to 2 liters of fuel, for example 0 liter or 1 liter.
Operating situations for the special mode, in which an internal combustion engine is not operated, are conceivable. For example, it may be the case that the internal combustion engine is not operated in the special mode when traveling downhill.
The one or more conditions for the special mode can comprise the condition that restarting of the hybrid vehicle by the driver is established in the vehicle. Restarting is triggered, for example, by means of an operator control action by the driver for switching off the ignition and by means of a subsequent operator control action by the driver for switching on the ignition, for example by first operation of a start/stop button for switch off and a second operation of the start/stop button for switch on; this sequence of the start/stop button is registered by the vehicle. Switch on and switch off of the ignition is also called a terminal change.
Therefore, if the driver triggers a terminal change, for example in the event of a lack of operational capability of the electric drive (for example in the case of breakdown), a special mode of the vehicle can be triggered as a result when the internal combustion engine is switched on.
In addition or as an alternative, the one or more conditions for the special mode can comprise at least one operating parameter of the electric drive, which is related to the operational capability of the electric drive, satisfying a criterion for reduced operational capability of the electric drive. For example, a condition for the special mode can be that the state of charge (SOC) is less than or less than or equal to a specific threshold value for the charge level.
For example, when the vehicle is restarted, a check can be made in respect of whether the charge level is less than or less than or equal to the threshold value for the charge level. If this is the case, the special mode is activated. Otherwise, the purely electric mode is activated for example.
A special mode is ended and the internal combustion engine is turned off when, preferably, a component diagnosis function establishes a lack of fuel and preferably requests the internal combustion engine be turned off on account of a lack of fuel. For example, the diagnosis function of the fuel high-pressure pump establishes that there is no longer any fuel, and therefore it requests the internal combustion engine be switched off. The internal combustion engine can therefore still be operated using the residual fuel for as long as possible, until virtually no more fuel is available.
A second aspect of the invention relates to a control device for controlling the operation of a hybrid vehicle comprising an internal combustion engine and an electrical machine for driving the hybrid vehicle. The control device is designed to establish that the fuel filling level sensor indicates that a lower filling level has been reached or undershot, and, in response to this, to trigger switch off of the internal combustion engine and driving of the vehicle in the purely electric mode, with the internal combustion engine switched off, by means of the electrical machine. The control device is characterized in that, after the purely electric mode of the vehicle, the control device is designed to trigger switch on of the internal combustion engine and driving of the vehicle by means of the internal combustion engine in the special mode with the internal combustion engine switched on, provided that one or more conditions for the special mode are satisfied.
The above statements relating to the method according to the invention in accordance with the first aspect of the invention apply in a corresponding manner to the control device according to the invention in accordance with the second aspect of the invention too. Advantageous exemplary embodiments of the control device according to the invention which are not explicitly described at this point and in the patent claims correspond to the advantageous exemplary embodiments of the method according to the invention described above or described in the patent claims.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.